Algorithm for decreasing the number of the unnecessary checkpoints in the cellular search

ABSTRACT

An algorithm for decreasing the number of the unnecessary checkpoints in the cellular search includes a first and second search ways of each of the processes of the present invention. All the first search ways are same and the second search ways are classified to different search modes by algorithm. The first search ways and the second ways are continually consecutively actuated, and stop when obtaining a broken condition or find a best block-matching, and obtain a best motion vector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an algorithm in the cellular search (CS), and more particularly to an algorithm for decreasing the number of the unnecessary checkpoints in the cellular search.

2. Description of Related Art

In video coding systems, the motion estimation plays a key role to remove temporal correlation between video pictures allowing information compression at reasonable video quality. At the same time, motion estimation is a very critical module of the encoder since it consumes most of the available computing time. Therefore, a fast and accurate block-based search technique is highly desirable to assure much reduced process delay while maintaining good reconstructed image quality. A straightforward block-matching algorithm (BMA) is the full-search (FS), which exhaustively searches for the accurate motion vector. The algorithm searches all locations in a specific search range and selects the position where the residual error of block-matching is minimized. Although it is optimal, such an approach results to have a high computational cost due to the high number operations that are involved, and it is not suitable for real time and low power applications. To overcome this drawback, many fast block-matching algorithms have been developed, for example, 2-D logarithm search (LOGS), three-step search (TSS), cellular search (CS), fast three-step search (FTSS), four-step search (4SS), diamond search (DS), etc., in which, cellular search is an efficient one in fast computation while keeping the reasonable picture performance.

The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional algorithms.

SUMMARY OF THE INVENTION

The main objective of the present invention is to provide an improved algorithm that decreases the number of the unnecessary checkpoints in the cellular search.

To achieve the objective, the algorithm in accordance with the present invention comprises a first and second search ways of each of the processes of the present invention. All the first search ways are same and the second search ways are classified to different search modes by algorithm. The first search ways and the second ways are continually consecutively actuated, and stop when obtaining a broken condition or find a best block-matching, and obtain a best motion vector.

Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an original step of an algorithm for decreasing the number of the unnecessary checkpoints in the cellular search in accordance with the present invention;

FIG. 2 shows a case 1 of the comparison processes of the present invention;

FIG. 3 shows a case 2 of the comparison processes of the present invention;

FIG. 4 shows a case 3 of the comparison processes of the present invention

FIG. 5 shows a case 5 of the comparison processes of the present invention;

FIG. 6 shows fifteen checkpoints of the algorithm of the present invention;

FIG. 7 is a flow chart of the algorithm of the present invention;

FIG. 8 is a processing chart of the algorithm of the present invention; and

FIG. 9 is a comparison list of the algorithm of the present invention and the conventional algorithm.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings and initially to FIG. 1, an algorithm for decreasing the number of the unnecessary checkpoints in the cellular search in accordance with the present invention comprises a first and second search ways of each of the processes of the present invention. All the first search ways are same and the second search ways are classified to different search modes by algorithm. The first search ways and the second ways are continually consecutively actuated, and stop when obtaining a broken condition or find a best block-matching, and obtain a best vector. The broken condition is established when the mean absolute distance (MAD) between the slated block and the current block is zero. The searching process of the slated block is stopped in advance, output a best motion vector of the slated block and search next current block. Consequently, to use the broken condition can effectively reduce the number of the blocks that needs to be searched, that's, the computation is reduced. The algorithm of the present invention is especially effective when being used to the pictures in slow motion. The MAD can be adjusted due to the characteristics of the videos.

The algorithm of the present invention includes the following steps.

STEP 1

The position of the current block is set as a center of searching region and has a coordinate (0, 0). According to the result of statistics, most of the video images have a motion vector that is near the origin of the coordinates. Consequently, for calculating the motion vector by CS, it will more quickly find the position of the motion vector from the center than that from the periphery. For the beginning, three possible slated blocks (13, 14, 15) in a 5×5 search window are compared and calculated the MADs thereof. The position of the slated block relative to the current block is recorded, and the difference and the motion vector are output when the MAD is zero. Otherwise, the step 2 is actuated.

STEP 2

The MADs of the above three slated blocks (13, 14, 15) are calculated and arranged after finishing the step 1, and selects a searching mode of the three slated blocks via the pseudo codes of the three slated blocks. The comparison processes are shown in FIG. 7.

Case 1, with reference to FIG. 2 If MAD (15) < MAD (13) < MAD (14) If MAD (15)=0 break end If MAD (15) < MAD (9) If MAD (9)=0 break end then check 1, 2, 3, 4 & select min{MAD(x)} If MAD (1)=0 break end If MAD (2)=0 break end If MAD (3)=0 break end If MAD (4)=0 break end else min{MAD(x)}=MAD (9) end end End

CASE 2, with reference to FIG. 3 If MAD (15) < MAD (14) <MAD (13) If MAD (15)=0 break end If MAD (15) <MAD (10) If MAD (10)=0 break end then check 5, 6, 7, 8 & select min{MAD(x)} If MAD (5)=0 break end If MAD (6)=0 break end If MAD (7)=0 break end If MAD (8)=0 break end else check 12 & select min{MAD(x)} end End

CASE 3, with reference to FIG. 4 If MAD (13) < MAD (15) < MAD (14) If MAD (13)=0 break end If MAD (11) < MAD (13) If MAD (11)=0 break end then min{MAD(x)}=MAD (11) else min{MAD(x)}=MAD (13) end End

CASE 4 If MAD (13) < MAD (14) < MAD (15) min{MAD(x)}=MAD (13) End

CASE 5, with reference to FIG. 5 If MAD (14) < MAD (15) < MAD (13) If MAD (14)=0 break end If MAD (12) < MAD (14) If MAD (12)=0 break end then min{MAD(x)}=MAD (12) else min{MAD(x)}=MAD (14) end End

CASE 6 If MAD (14) < MAD (13) < MAD (15) min{MAD(x)}=MAD (14) End

The algorithm of the present invention locations in a specific search range and selects the position where the residual error of the block matching is minimized. Consequently, the algorithm contains the modes and the characteristics of all the conventional algorithm searches. The slated blocks of the large cellular search pattern (LCSP) are effectively reduced by comparing the three original slated blocks. The LCSP mode is changed into a small cellular search pattern (SCSP) mode for searching eight slated blocks when using the LCSP mode and the MAD is found on the center point. The algorithm of the present invention has a mode similar to that of CS. When processing the present invention and the MAD is found on the center point, the blocks surround the center point will be searched. However, the number of the slated block is reduced from eight to four. Consequently, the processing time of the present invention is faster than that of the conventional algorithms.

The video quality must to be considered in the algorithm. The conventional algorithms usually use peak signal to noise ratio (PSNR) to estimate the video quality, as shown in the following formula: ${{PSNR} = {10\quad\log_{10}\frac{255 \times 255}{\frac{1}{N \times N}{\sum\limits_{x = 1}^{N}{\sum\limits_{y = 1}^{N}{{{f\left( {x,y} \right)} - {f^{\prime}\left( {x,y} \right)}}}^{2}}}}}},$ wherein the f(x,y) is the original picture.

In the following experiment, three standard videos (salesman, football and susigirl) are selected, wherein the moving object in each of the above videos has a moving speed. The football video is the first, the susigirl is the secondary and the salesman is the third relative to the moving speed of the moving object therein. Each standard video contains fifty pictures each with a size: 352×288 pixels, grayscale: 8 bits, searching scope: −7 to +7 and a block size: 16×16 pixels. The MAD is used to judge that the minimized distortion block is found or not and the effects of the CS and TSS is compared.

With reference to FIG. 9, table 1 to table 3, the performance evaluation items include MSE (mean square error), PSNR and Average Points.

In PSNR: the performance of the algorithm of the present invention is similar to the CS in the Salesman video and the Sugigirl video, and better than that of the TSS. However, in the Football video, the video quality of the TSS is better than that of the present and the CS.

In MSE: in Football video, the performance of the TSS is lower than that of the CS and the present invention. In the salesman video and the Susigirl video, the effects of the present invention and the CS are similar to each other and within an acceptable scope.

In the Average Points: the present invention reduces the number of the checkpoint of the CS about 50%, that's, the algorithm has a low computation rate.

Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed. 

1. A algorithm for decreasing the number of the checkpoints in the cellular search, comprising a first and second search ways of each of the processes of the algorithm, all the first search ways being same and the second search ways being classified to different search modes by the algorithm, the first search ways and the second ways continually consecutively actuated, and stopped when obtaining a broken condition or find a best block-matching, a best motion vector obtained by comparing slated blocks.
 2. The algorithm as claimed in claim 1, wherein a method for finding the block-matching comprises the following steps of: selecting three original slated areas in the searching scope, finding a searching slated area by comparing the three original slated areas; six cases being used a single path and selected due to the three original slated areas; and searching the block-matching to decide the last motion vector of the referring block, the searching slated area having a center used to continually actuate searching process and stopped when obtaining a broken condition or find a best block-matching, and outputting the last motion vector.
 3. The algorithm as claimed in claim 2, wherein the broken condition is established when a mean absolute distance (MAD) is zero. 